First thing first
1. Don't try to invest your hard earned money in one go.
2. Don't trust anyone: Any individual who trying to selling bitcoinonline because there are lots of scammers around in crypto world ( unless you know the person in real and trust him/her)
3. if you wanna buy then you can use exchange directly there are many decentralized and centralized you name it. to name a few:
    (A) Localbitcoin : https://localbitcoins.com/
    (B) Binance       : https://www.binance.com/
    (C) Bittrex         : https://bittrex.com/
    (D) Idex            : https://idex.market/eth/aura ( Decentralized)
    (E) Forkdelta      : https://forkdelta.github.io/

NOTE : you can't buy bitcoin in last 2 exchange( Only for erc20 tokens) but they are decentralized.